1. Field of the Invention
The present invention relates to a multi-beam exposer unit, which can be used in a color printer having a plurality of drums, a color copy machine having a plurality of drums, a high-speed laser printer or a digital copy machine, for scanning a plurality of beams.
2. Description of the Related Art
In an image forming unit such as a color printer having a plurality of drums or a color copy machine having a plurality of drums, there are used a plurality of image forming sections for forming an image in accordance with color components, which are color-separated, and a laser exposer unit for providing a plurality of image data, i.e., a plurality of laser beams for every color component. As a laser exposer unit, there are known an example in which a plurality of laser exposer units are arranged and an example in which a multi-beam laser exposer unit, which is structured to be able to provide a plurality of laser beams.
In Japanese Patent Application KOKAI Publication No. 5-83485, there is an example using N sets of a light source, a cylinder lens, and glass fxcex8 lens groups, and N/2 of polygon mirrors wherein the number beams is N. For example, in the case of four beams, four sets of the light sources, the cylinder lens glass fxcex8 lens groups, and two polygon mirrors are used.
Moreover, for example, there is proposed an example of using a lens of a part of the fxcex8 lens group in common. In other words, there is proposed a method in which two groups of fxcex8 lens are set, all laser beams are passed through the fxcex8 lens close to the polygon mirror, the number of fxcex8 lenses far away from the polygon mirror is set to four, and each laser beam is individually passed through each lens.
Separately from the above examples, Japanese Patent Application KOKAI Publication No. 62-232344 discloses an example in which at least a part of a lens surface of the fxcex8 lens is formed to have a toric surface to be used in common. Also, in Japanese Patent Application KOKAI Publication No. 62-232344, there is proposed that several fxcex8 lenses are formed of plastic to improve a degree of design freedom of each lens surface and an aberration characteristic at an image-forming position. Japanese Patent Application KOKAI Publication No. 62-232344 also discloses a method in which each lens is used in common and all laser beams are passed through each lens.
Japanese Patent Application KOKAI Publication No. 5-83485 shows an apparatus in which the members corresponding to four sets of laser beam exposure units are incorporated into one housing. As compared with a case of using a plurality of laser beam exposer units, the space which is occupied by the laser exposer unit, is reduced in the case of using the multi-beam laser beam exposer unit seen in Japanese Patent Application KOKAI Publication No. 5-83485. However, from the viewpoint of the single laser exposer unit, the cost of parts and that of the assembly rise due to an increase in the number of lenses or the number of mirrors. Moreover, the size and weight as a single unit are increased. Furthermore, it is known that a curve of the main scanning line of the laser beam of each color component or deviation of the aberration characteristic on the image-forming surface such as a fxcex8 characteristic becomes uneven due to deviation of the manufacture of the same fxcex8 lenses, an error included in individual fxcex8 lenses, or an error of the attachment.
Moreover, in the case of Japanese Patent Application KOKAI Publication No. 62-232344, since only the toric surface whose shape is not optimized is provided, there is a problem in that curve of the main scanning line is generated in any of the plurality of laser beams. There is also proposed an example in which a part of the laser beam directing to a deflector is controlled to be directed to a direction of an optical axis. However, it is difficult to sufficiently compensate for the aberration characteristic in all image-forming areas. Moreover, a refractive index of the lens formed of plastic is relatively largely changed by the change of temperature. Due to this, field curvature, curve of the main scanning line, or the fxcex8 characteristic vary largely under environmental conditions over a wide range, particularly a state that the temperature condition is changed, there occurs a problem in which a field curvature, and a curve of the main scanning line, or the fxcex8 characteristic vary largely. Moreover, in the case of Japanese Patent Application KOKAI Publication No. 62-232344, conditions such as achromatism on the entire area of the sub-scanning direction, curvature, distortion of the image surface, and a lateral magnification are not satisfied. Due to this, the number of lenses is increased. Furthermore, since the accuracy of the housing must be extremely highly set in order to ensure parallelism of the main scanning line of each laser beam, the manufacturing cost rises.
An object of the present invention is to provide a multi-beam laser exposer unit, which can be applied to the image forming unit for forming a color image in proper registration, with low cost.
Another object of the present invention is to provide a multi-beam laser exposer unit which does not need complicated adjustment.
Moreover, another object of the present invention is to provide a multi-beam exposer unit, which is not subjected to influence of deviation between the beams, that is, an error included in individual fxcex8 lenses.
According to a first aspect of the present invention, there is provided a multi-beam laser exposer unit comprising: a plurality of light beam sources for emitting light beams; deflecting means, having reflective surfaces formed to be rotatable, for deflecting light beams emitted from the light beam sources in a predetermined direction; pre-deflection optical means for converting each light beam emitted from each light beam source to a convergent light beam in a direction parallel to a rotational axis of each surface of the deflecting means, and to a convergent light beam or a parallel light beam in a direction perpendicular to the rotation axis of each surface of the deflecting means so as to be guided to the reflective surfaces of the deflecting means; and post-deflection optical means having two lenses, each of the lenses having a function of image-forming each of the light beams deflected by the deflecting means to be scanned on a predetermined image surface at a uniform speed, and a function of correcting influence of variation of an inclination of the reflective surface on a position of the light beam on the image surface, being exerted onto each of the light beams, expressed as deviation of an angle formed between the reflective surface of the deflector and the rotational axis of the reflective surface, each of the lenses having positive power in a direction parallel to the rotational axis of each surface of the deflecting means, and each light beam crossing each other between the lenses in the direction parallel to the rotational axis of each surface of the deflecting means.
According to a second aspect of the present invention, there is provided a multi-beam laser exposer unit comprising: a plurality of light beam sources for emitting light beams; deflecting means, having reflective surfaces formed to be rotatable, for deflecting light beams emitted from the light beam sources in a predetermined direction; pre-deflection optical means for converting each light beam emitted from each light beam source to a convergent light beam in a direction parallel to a rotational axis of each surface of the deflecting means, and to a convergent light beam or a parallel light beam in a direction perpendicular to the rotation axis of each surface of the deflecting means so as to be guided to the reflective surfaces of the deflecting means; and post-deflection optical means having two lenses, each of the lenses having a function of image-forming each of the light beams deflected by the deflecting means to be scanned on a predetermined image surface at a uniform speed, and a function of correcting an influence of variation of an inclination of the reflective surface on a position of the light beam on the image surface, being exerted onto each of the light beams, expressed as a deviation of an angle formed between the reflective surface of the deflector and the rotational axis of the reflective surface, and at least one lens surface of four lens surfaces of each of the lenses is formed on a portion other than a rotational symmetrical surface.
According to a third aspect of the present invention, there is provided a multi-beam laser exposer unit comprising: a plurality of light beam sources for emitting light beams; deflecting means, having a rotatable axis and reflective surfaces formed to be rotatable around the rotational axis, for deflecting light beams emitted from the respective light beam sources as substantially one light beam in a predetermined direction; pre-deflection optical means, provided between the deflecting means and each of the light beam sources, for converting each light beam emitted from each light beam source to a convergent light beam in a direction parallel to a rotational axis of each surface of the deflecting means, and to a convergent light beam or a parallel light beam in a direction perpendicular to the rotation axis of each surface of the deflecting means so as to be guided to the reflective surfaces of the deflecting means; and post-deflection optical means having two lenses, each of the lenses having a function of image-forming each of the light beams deflected by the deflecting means to be scanned on a predetermined image surface at a uniform speed, and a function of correcting influence of variation of an inclination of the reflective surface on a position of the light beam on the image surface, being exerted onto each of the light beams, expressed as deviation of a angle formed between the reflective surface of the deflector and the rotational axis of the reflective surface, each of the lenses having positive power in a direction parallel to the rotational axis of each surface of the deflecting means, each light beam crossing each other between the lenses in the direction parallel to the rotational axis of each surface of the deflecting means and at least one lens surface of four lens surfaces of each of the lenses is formed on a portion other than a rotational symmetrical surface.
According to a fourth aspect of the present invention, there is provided a multi-beam laser exposer unit, comprising: deflecting means, having reflective surfaces formed to be rotational, for deflecting light beams emitted from a plurality of light beam sources in a predetermined direction; pre-deflection optical means for converting each light beam emitted from each light beam source to a convergent light beam in a direction parallel to a rotational axis of each surface of the deflecting means, and to a convergent light beam or a parallel light beam in a direction perpendicular to the rotation axis of each surface of the deflecting means so as to be guided to the reflective surfaces of the deflecting means; post-deflection optical means having two lenses, each of the lenses having a function of image-forming each of the light beams deflected by the deflecting means to be scanned on a predetermined image surface at a uniform speed, and a function of correcting an influence of variation of an inclination of the reflective surface on a position the light beam on the image surface, being exerted onto each of the light beams, expressed as a deviation of an angle formed between the reflective surface of the deflector and the rotational axis of the reflective surface; and mirror members for separating the respective light beams passed through the post-deflecting optical means, wherein the deflecting means deflect the light beam directing to one of the mirror members provided at a position closest to an image surface and the light beam directing to one of the mirror members provided at a position secondly closest to an image surface at a narrowest distance in a direction parallel to the rotational axis of the surface of the deflecting means.
According to a fifth aspect of the present invention, there is provided a multi-beam laser exposure unit comprising: a plurality of light beam sources for emitting light beams, the respective light beam sources provided in a second direction perpendicular to a first direction to have a different distance, and directed to a different direction from each other in a plane including the first direction; a combined mirror, having reflective surfaces whose number is smaller than the number of the light beam sources by one, for directing each of light beams emitted from the light beam sources in the same direction of the first direction; deflecting means, having reflective surfaces formed to be rotatable in the first direction, for deflecting the respective light beams emitted from the respective light beam sources and combined by the combined mirror in a predetermined direction; pre-deflection optical means for converting each light beam emitted from each light beam source to a convergent light beam in a direction parallel to a rotational axis of each surface of the deflecting means, and to a convergent light beam or a parallel light beam in a direction perpendicular to the rotation axis of each surface of the deflecting means so as to be guided to the reflective surfaces of the deflecting means; and post-deflection optical means having two lenses, each of the lenses having a function of image-forming each of the light beams deflected by the deflecting means to be scanned on a predetermined image surface at a uniform speed, and a function of correcting an influence of variation of an inclination of the reflective surface on a position of the light beam on the image surface, being exerted onto each of the light beams, expressed as a deviation of an angle formed between the reflective surface of the deflector and the rotational axis of the reflective surface, wherein each of normal lines of the mirror surfaces of the combined mirror are arranged at a different angle to a line connecting the deflecting means to a non-reflected light beam source, whose light is not reflected by the combined mirror, and a mirror surface of the combined mirror reflects a light beam separated nearest from a light beam emitted from the non-reflected light beam source.
Additional objects and advantages of the invention will be set forth in the description which follows, and in part will be obvious from the description, or may be learned by practice of the invention. The objects and advantages of the invention may be realized and obtained by means of the instrumentalities and combinations particularly pointed out in the appended claims.